This blog discusses current weather, weather prediction, climate issues, and other topics

Sunday, April 3, 2011

Radioactivity Measurements

During the past few days a great deal of information has come in about the amount of radiation reaching the U.S. from the Fukushima reactors in Japan. Measurable radiation has reached our shores, but thousands of times below intervention standards.

Recently, a University of Washington team presented highly sensitive results based on measuring the radioactive particles trapped by the filters for the UW Physics and Astronomy Building (their web site is http://www.npl.washington.edu/monitoring/).

Let me show you some examples of their findings and remember the tsunami occurred on March 11. Here is a plot of the amount of radiation measured on 16 March and 17 March, based on the energy levels associated with Iodine-131. The signal is very clear on 17 March.

Here is an alternative presentation for more radioactive species. A clear signal was evident around 7 days after the tsunami, peaking a few days later, and then declining.Again, these levels, although measurable are very low and not a threat.

EPA has been actively taking samples of rainwater and milk around the country. The rainwater results, released yesterday, revealed that for most of the country the radioactivity increase was unmeasurable except for Richmond, CA, Boise, Id. and St. Paul, Mn. Boise was particularly high. WHY?

But keep in mind that we generally don't drink rainwater and I131 has a half life of eight days. By the time water is used (either percolating to the water table and entering a well or reaching the intake of a reservoir--where it has hugely been diluted--little I 131 radioactivity will be left.

A number of the media is hyping the radioactivity levels by making the implicit assumption that the relatively high values will continue for an entire year...which of course is ridiculous. A few locations in the U.S. have had some one-day spikes, but the dosage would be very low...even if you drank rainwater...because radioactivity levels rapidly drop down into the noise level.

Regarding milk, screening samples taken March 25 at Spokane, WA detected 0.8 pCi/L of iodine-131, which is more than 5,000 times lower than the Intervention level set by the U.S. Food and Drug Administration.

The fact that some of the radiation has reached the NW in minute quantities should not surprise us. Several scientists (such as Dr. Dan Jaffe of the UW) regularly measure small amounts of Asian pollution over the Northwest, particularly as specially equipped labs at Cheeka Peek (NW Washington) and Oregon's Mt. Bachelor.

The maximum level of 131I we observed in the rainwater was 430 pCi/liter (16 Bq/liter)from the sample collected on March 24. This maximum activity can be compared to the USEPA limit (5) on 131I allowed in drinking water of 108 pCi/liter. If a person were to drink atypical amount of water per day containing the EPA limit of 131I, then in one year he or shewould receive a whole body dose of < 0.04 mSv (4 mrem). This dose should be compared to theUS average annual radiation dose of 6.2 mSv (620 mrem) (6). Due to the short half life of 131I,it is extremely unlikely that the public will be exposed to anywhere near these levels in drinkingwater. Thus the levels of fallout we have observed in San Francisco Bay area rain water pose nohealth risk to the public.

I agree with your premise that the amounts detected are minuscule, but I interpret the published EPA data differently.

It is not clear that the published data represent the ONLY sampling sites where a radioactivity increase attributable to the Fukushima disaster was measurable (e.g., the EPA previously reported elevated levels of I-131 in PA and MA rainwater samples, but this data is omitted). The EPA gives no rationale for why they chose to report data for these selected sites as opposed to others.

The UC Berkeley Nuclear Engineering Dept. is prublishing much more detailed analysis of air, rain and tap water concentrations. The reported rainwater concentrations of I-131 on March 24th were in the vicinity of 540 pCi/L (http://www.nuc.berkeley.edu/RainWaterSampling), or roughly 3x the concentration reported by the EPA for Boise.

A colleague from the East Coast sent out this email to us today: "be advised that on April 6th models show that Seattle will get a big hit of an air mass which has traveled more intact than normally from Fukushima. That may be a good day to reduce exposure to outdoor dusts."

He didn't say anything about panicking or hiding inside no matter what, but just that - to avoid outdoor dust. What have you heard on this and will the levels be anywhere near even background levels of radiation even on that day?

I'm not too worried about the radiation. The westerly flow really has kept us dry in north kistap county. I went through the car wash yesterday :) Went to Port Townsend yesterday and ate at Sirens. A good escape. Pt. Wilson had S15G20, but a nice day to be outside! Hope everyone had a nice weekend.

Your data are reassuring. I just wonder what it be look like however if there had been (or is in the future) a meltdown at one (or more) of the reactors or if the stored fuel rods had caught on fire. I would think in these cases the release to the environment would potentially be many orders of magnitude greater than its been so far. What this would mean to us here.. not sure.

My question is, should I give my chickens, who drink water from the rain barrel, iodine tablets? Radioactivity is much more harmful when ingested, so I wonder if the eggs could contain some of the I-133. Probably not a concern with an 8 day half life, but it did cross my mind.

Cowgrrl, acid rain is different from radioactivity. It was mostly generated from industrial pollution resulting from fossil fuel processing. Strict air standards have brought it under control.